Gas turbines are widely used in industrial and power generation operations. A typical gas turbine may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the air to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The fuel supplied to the combustor may be a liquid fuel, a gaseous fuel, or a combination of liquid and gaseous fuels. For example, possible liquid fuels supplied to the combustor may include fuel oil, naptha, petroleum, coal tar, crude oil, and gasoline, and possible gaseous fuels supplied to the combustor may include blast furnace gas, coke oven gas, natural gas, methane, vaporized liquefied natural gas (LNG), hydrogen, syngas, and propane. If the liquid and/or gaseous fuel is not evenly mixed with the air prior to combustion, localized hot spots may form in the combustor. The localized hot spots may increase the production of undesirable NOx emissions and may increase the chance for the flame in the combustor to flash back into the nozzles and/or become attached inside the nozzles which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and a wider flammability range.
A variety of techniques exist to allow higher operating combustor temperatures while minimizing NOx emissions, flash back, and flame holding. Many of these techniques seek to reduce localized hot spots to reduce the production of NOx and/or reduce low flow zones to prevent or reduce the occurrence of flash back or flame holding. For example, continuous improvements in nozzle designs result in more uniform mixing of the fuel and air prior to combustion to reduce or prevent localized hot spots from forming in the combustor. Alternately, or in addition, nozzles have been designed to ensure a minimum flow rate of fuel and/or air through the nozzle to cool the nozzle surfaces and/or prevent the combustor flame from flashing back into the nozzle. However, the improved nozzle designs typically result in increased manufacturing costs and/or continued additional parts or components added to the combustor that increase the differential pressure across the combustor, thus detracting from the overall efficiency of the gas turbine. Therefore, improvements in combustor designs to enhance the mixing of fuel and air prior to combustion and/or cool the combustor surfaces would be useful. In addition, combustor designs that may readily switch between various combinations of liquid and gaseous fuels would be useful.